By BILL PENNINGTON

Felix Trinidad, who moved up in class to middleweight, is scheduled to fight Bernard Hopkins in a unification bout at the Garden.

A century of professional boxing history would suggest that fighters moving up one, two or even three weight classes to challenge larger opponents do so at their own peril. Felix Trinidad is reversing the formula. When Trinidad visits a new division, everyone else suddenly looks smaller.

The undefeated Trinidad's ascent through boxing's ranks has been audacious in its efficacy, a blur of upright punching and ingenuous tactics of angle and leverage. Trinidad, the longtime welterweight champion, has added 13 pounds and now commands the middleweights. The light-heavyweight Roy Jones Jr. could be next. Even the heavyweights may yet experience Trinidad's combination of proficiency, power and poise.

With the 28-year-old Trinidad, anything seems possible.

His dismantling of the middleweight champion William Joppy late Saturday night at Madison Square Garden was a striking, almost frightening, display of Trinidad's potential. Trinidad was making his first fight at 160 pounds and across the ring was a scrappy, smart, seasoned champion in Joppy, who was making the eighth defense of his World Boxing Association title.

Trinidad, a notoriously slow starter, even let Joppy dictate the pace of the first two minutes of the fight. What followed was dazzling, a series of Trinidad punch combinations delivered from a variety of directions and with little discernible pattern. For the last 30 seconds of the first round  when Joppy was knocked down for the first time  and for parts of the four rounds that came after, Trinidad dominated Joppy in a way that made it plain that Trinidad has few peers in his sport.

Trinidad decked Joppy three times in the fight until Referee Arthur Mercante Jr. called an end to the bout as Joppy wobbled face first into a ring post with 35 seconds remaining in the fifth round. Joppy, a sturdy, confident 30-year-old who is proud of his 32-2-1 record, said afterward, "I've never been hit like that in my life."

Trinidad both attacked and fought effectively with counterpunches. He knocked Joppy down in the first round with a left hook  set up by a chopping right. Trinidad ended the fight with a stinging overhand right  and another right as Joppy was crashing to the canvas on his side and head. In between, early in the fourth round, Joppy was sent tumbling backward  he nearly did a somersault  with two right hands to the head and a sweeping left hook.

What made Trinidad's domination more impressive was that Joppy somehow kept righting himself well enough to keep fighting and press the action. Gritty and courageous, Joppy might have even won the third round when a computer counted his punch total at 116.

But Trinidad waited and sent Joppy scrambling and sprawling again and again.

"I told you, I promised you I would show you that I am a true middleweight," Trinidad said afterward. "I showed you a champion's performance."

Few disagreed, even Bernard Hopkins, the World Boxing Council and International Boxing Federation champion who will be Trinidad's next opponent, Sept. 15 at the Garden. That is the last fight in the series to unify the middleweight division.

Hopkins conceded Trinidad fought a terrific fight, but since he has to fight him next, he also found some brave words to hype his own confrontation.

"I beat Trinidad by making it a street fight  elbows and knees," Hopkins said. "I am not William Joppy. I am not 5 feet 9 like Joppy, I am 6-feet tall. He won't be punching down on me. I'm the true champion."

If that sounded like typical boxing bluster, it only got worse. With a nod to the thousands of Puerto Rican fans who feted their native son Trinidad with flags and drums at the Garden, Hopkins, whose nickname is the Executioner, said: "We fight on Sept. 15. On Sept. 16, Puerto Rico is going to have a flag at half-mast. That's how serious this is to me. Again, get ready to lower your flags to half-mast."

Told of Hopkins's comments, Trinidad had little reaction.

"In Joppy, I have already beaten the best middleweight," Trinidad said, repeating an opinion that was the consensus in the boxing community. "Bernard Hopkins has been a great champion, but now it's his time. I will do the same to him that I did to William Joppy."

It is worth noting that before Saturday's fight, Trinidad said he would do the same to Joppy that he did to Oscar De La Hoya, David Reid and Fernando Vargas. Trinidad defeated each, but much more convincing is how Trinidad seems to be getting stronger and more effective with each new challenge.

Trinidad, undefeated in 40 fights, a champion now in three weight classes and a titleholder since 1993, appears to be getting better as he gets older. Another formula reversed.